Orthoses for Spinal Deformities

Pathophysiology and Natural History

Idiopathic scoliosis (IS), termed as such because of the unknown cause or etiology of the deformity, is the most common form of scoliosis. A thorough physical examination by a qualified physician, including a radiographic analysis to rule out numerous potential differential diagnoses, is required to make the diagnosis. The type of idiopathic scoliosis is defined by the age of onset. If scoliosis is recognized in a patient younger than 3 years of age, it is considered infantile idiopathic scoliosis. Scoliosis detected between the ages of 3 and 10 years is considered juvenile idiopathic scoliosis. The most common form of idiopathic scoliosis is adolescent idiopathic scoliosis (AIS), which includes curvature detected at age 10 years but before skeletal maturity. A scoliosis that is detected after skeletal maturity is classified as adult scoliosis.

Because of the relationship between the rate of spinal growth and the progression of deformity, the terms early-onset idiopathic scoliosis (EIS) and late-onset idiopathic scoliosis (LIS) have come into favor. Two primary periods of rapid growth occur in the first few years of life and then again during the adolescent growth spurt. Mehta pointed out that the fastest rate of growth in children is in the first year of life, with a growth rate of 20 to 25 cm in those 12 months, versus the adolescent growth spurt, where growth of 12 to 14 cm per year can be seen. An increase in height at the rate of 9 cm per year is considered a reasonable threshold to identify this peak period during adolescence. With regard to the specific growth velocity of the spine as measured between the T1 and L5 segments, it is greatest from birth to age 5 years and then again between the ages of 10 years and the onset of puberty. For this reason, the term early-onset scoliosis has been used to reflect the presence of scoliosis before 5 years of age, including all possible etiologies, whereas the term late-onset scoliosis applies to scoliosis detected after age 5 years and is most commonly associated with adolescent scoliosis.

Some critical differences exist between the prognosis of patients with EIS and of those with LIS. EIS is diagnosed within the first 6 months of life in most children, is seen more often in boys than in girls (with most having left-sided thoracic curve patterns), and has the capacity to spontaneously resolve in some patients. The most reliable indicators for differentiating resolving scoliosis from progressive scoliosis are the rib–vertebra angle difference (RVAD), which is the angular difference between the concave and convex side ribs in relation to the apical thoracic vertebra, and the amount of apical vertebral rotation, as defined by phase I and phase II rotation ( Fig. 8.1 ). It has been demonstrated in several studies that an RVAD of less than 20 degrees indicates a high likelihood of curve resolution, whereas curves with an RVAD of 20 degrees or greater are more likely to be progressive. A phase 2 relationship ( Fig. 8.2 ) between the rib head and apical vertebra on the convex side implies that progression of the curve is almost certain.

Pulmonary compromise is a much more significant concern in those diagnosed with EIS compared with those with LIS. This is because of the presence of a potentially progressive chest wall deformity associated with the scoliosis during the time in which the lungs are rapidly developing. There is a significant increase in the number of alveoli and respiratory branches, with most of this increase occurring during the first 8 years of life. The incomplete maturation of the lung and pulmonary vasculature has been reported as the primary reason for ventilation defects seen in patients with early-onset scoliosis. Though still being researched, there is an apparent correlation between the age of scoliosis onset and the diminished number of alveoli that develop with the most hypoplastic lungs are found in those with the earliest onset of EIS. Reduction of vital capacity can be seen from compressive forces and is influenced by the location and severity of the curve. This poor respiratory development places these patients at greater risk for life-threatening respiratory failure at or before middle age. This is unique to these young patients, because those with LIS demonstrate little or no reduction of vital capacity in response to the presence of their curve.

Understanding the natural history of LIS is essential to clinical decision-making. This is true not only for determining when observation or treatment is indicated but also for determining when treatment is effective. AIS is the most common form of idiopathic scoliosis, affecting 1.5% to 3.0% of children who are at least 10 years of age. Curves exceeding 20 degrees affect between 0.3% and 0.5%, and curves exceeding 30 degrees are found in 0.2% to 0.3% of adolescents. Curve progression is typically defined as a measured difference of 5 degrees or greater ; however, a 10-degree change has been reported as being required for 95% certainty that an observed change was not caused by measurement error alone, but is instead indicative of true progression.

Fewer than 1% of children screened for scoliosis and fewer than 10% of those who are positively identified as having a curve of at least 10 degrees will require active treatment. Debate continues regarding the appropriateness of regular screening of adolescents with consideration to the financial burden of monitoring and the radiation exposure to the child, because a large percentage of children never require active treatment. The goal of an evaluating physician is to make an accurate diagnosis and to identify which patients are most likely to progress and thus require treatment, either with an orthosis or with surgery. Notably, research is still inconclusive regarding which intervention is most indicated for AIS curves of greater than 45 degrees, and further research is required in this area. When prescribed, the goal of the orthosis is to prevent further progression of a curve that would otherwise worsen if left untreated. Factors that have the most influence on whether a curve secondary to AIS will progress are patient gender, remaining growth, curve magnitude, and curve pattern. Specific physical therapy protocols have been proposed, although the literature does not support this intervention as a reliable measure to effectively prevent curve progression.

With respect to gender, the prevalence of AIS is similar in boys and girls with smaller curves, but girls are more likely to experience curve progression. Boys with comparable curves have been estimated to have about one tenth the risk of curve progression as girls ; however, one report suggests the difference is less.

The amount of growth remaining is typically estimated by two maturity indices: the Risser sign and, in girls, the onset of menstruation; however, the single most accurate indicator is to monitor growth. The Risser sign is a skeletal marker based on the ossification of the iliac apophysis. It is interpreted by viewing a standing posteroanterior radiograph of the spine and pelvis, where ossification of the pelvis begins laterally and progresses medially until maturation ( Fig. 8.3 ).

The range of the Risser sign is from 0 to 5, with 0 indicating no ossification and 5 indicating a fully ossified ilium, which indicates skeletal maturity. A Risser sign of 0, 1, or, to a lesser extent, 2, is indicative of significant growth remaining, which can equate to a greater risk for curve progression in some patients with AIS. Some studies have questioned the usefulness of the Risser sign as a reliable measurement of skeletal maturity, including reports of differing interpretations on how the excursion of the iliac apophysis is scored. In girls, the onset of the menstrual cycle is a physiologic indicator that is helpful in estimating remaining growth. After menarche girls enter the deceleration phase of growth, during which curve progression becomes less likely.

A third indicator of skeletal maturity, the peak height velocity (PHV), is more difficult to immediately assess than the Risser sign or menarchal status in girls, but it has gained greater recognition as a more accurate tool to assess the amount of growth remaining in an adolescent with idiopathic scoliosis. PHV is calculated from changes in a patient's height measurements over time, typically recorded in intervals of no less than 4 and not more than 6 months. The average PHV has been reported as about 8.0 cm per year for girls and 9.5 cm per year for boys in the groups studied.

Little et al. reported on the relationship of growth rates, as expressed in overall height velocities, to other maturity indicators in girls with AIS. The timing of PHV, also known as peak growth age (PGA), was plotted against other maturity indicators, including chronologic age, Risser sign, and menarchal status, to determine its usefulness as a prognostic tool for curve progression. PGA was found to have a stronger correlation with curve progression than any other maturity indicator (age, Risser sign, or menarchal status). The usefulness of PGA as a clinical tool in boys with AIS has also been reported.

The size of a curve at the time of detection combined with estimating the degree of maturity is very helpful in predicting the risk for progression in AIS. Lonstein and Carlson described three primary prognostic factors in predicting curve progression in a growing child: curve size, chronologic age, and Risser sign. They reported that the younger the child, the lesser the Risser sign, and the larger the curve at discovery, the higher the likelihood for curve progression. A scoliosis that reaches a magnitude of 25 degrees in an immature patient, even if detected during an initial visit, typically is considered a candidate for orthotic treatment.

Natural history studies also have reported the usefulness of curve pattern in predicting curve progression. Opinion in the literature tends to agree that single lumbar and single thoracolumbar curves are the least likely to progress and are the most receptive to brace treatment. Compiling data from various natural history studies, Bunch and Patwardhan reported single thoracic and double curve patterns are more likely to progress (by as much as a factor of two) than single lumbar or single thoracolumbar curve patterns.

Orthoses should be used in patients whose curve size and pattern, if successfully stabilized, would be both cosmetically acceptable and functionally stable throughout adulthood. Weinstein and Ponsetil reported in a longitudinal study of 102 patients with untreated scoliosis over 40.5 years that 68% of the curves progressed after skeletal maturity. Curves of less than 30 degrees at skeletal maturity tended not to progress regardless of curve pattern, and those greater than 30 degrees appeared to be related to the amount of vertebral rotation. Curves that measured between 50 and 75 degrees progressed the most. Weinstein et al. studied outcomes related to health and general function in patients with untreated AIS. The authors compared 117 prospectively evaluated, untreated patients with 62 age- and sex-matched volunteers. Reporting on 50 years of follow-up, this review stated that those with LIS were more likely to experience back pain and, for those with thoracic curves greater than 80 degrees, shortness of breath compared with controls. There was no significant difference in the estimated probability of survival between the two groups. Others have cited no difference in mortality rate between patients with AIS and the general population. Thus the authors concluded that untreated adults with LIS demonstrated little physical impairment other than back pain and cosmetic concerns compared with age- and sex-matched controls. Chronic low-back pain is more common in adults with scoliosis, but it does not interfere with a patient's ability to work or perform activities.